1. Field of the Invention
This invention generally relates to the manufacturing of flat glass, and more particularly to a new and novel system for accurately aligning conveyor rolls employed in the processing of flat glass.
2. Description of the Prior Art
In the manufacture of flat glass, it is customary to produce a continuous ribbon of glass from a molten glass mass by one of the well-known sheet, plate or float glass forming processes, and convey this newly formed ribbon through an annealing lehr. The primary purpose of conveying the newly formed glass ribbon through the lehr is to cool it from the highly heated plastic condition in which it emerges from the forming area to a rigid glass ribbon at approximately ambient temperature while producing a controlled permanent stress pattern therein. In a conventional annealing process, temperatures in the lehr may range from about 1300.degree. F. (704.4.degree. C.) at its entrance end to about 400.degree. F. (204.4.degree. C.) or less at its exit end. The glass ribbon is gradually cooled in accordance with a predetermined pattern from the higher temperature level to the lower temperature level in order to produce a predetermined desired stress pattern in the glass ribbon. Accordingly, the lehrs employed in the production of flat glass may range in length from approximately 430 feet, 131.1 m to 650 feet, 198.1 m and may employ anywhere from two hundred and forty one (241) to three hundred forty six (346) transversely extending, longitudinally spaced conveyor rolls along such lengths.
The conveyor rolls must be properly aligned for preventing damage to the glass ribbon as it is conveyed through the lehr. If the rolls are not properly aligned, that is, if they are skewed relative to each other either in horizontal or vertical directions or combinations thereof, they may cause wrinkling or snaking of, and surface abrasions on, the glass ribbon rendering the glass unfit for commercial use. Also properly aligned rolls help keep the glass ribbon in the center of the lehr as it passes therethrough.
In the past, surveying techniques, including the use of levels, level rods and measuring tapes, have been used for aligning such conveyor rolls. Since the rolls require individual alignment, the utility of surveying techniques as an ultimate tool in aligning them is limited in that the exercise of human judgment is involved in reading and recording. One factor which limits the accuracy of such an alignment system is the setting of the surveying instruments from roll to roll. Another factor limiting the accuracy of such a system is the temperature of the environment surrounding the lehr, which is normally in the neighborhood of 140.degree. F. (60.degree. C.). This temperature, of course, causes the tape to change in length and since the temperature along each side of the lehr may be different the length of the tape will be different.